1. Technical Field
This disclosure relates to nanoimprint resist, nanoimprint mold and nanoimprint lithography.
2. Description of Related Art
In fabrication of semiconductor integrated electrical circuits, integrated optical, magnetic, mechanical circuits and micro devices, and the like, are some of the key processing methods is the lithography. Lithography creates a pattern in a thin film located on a substrate, so that, in subsequent process steps, the pattern will be replicated in the substrate or in another material located on the substrate. Since the role of the thin film is to protect a part of the substrate in the subsequent replication steps, the thin film is called resist.
Nanoimprint lithography (NIL) is a method of fabricating nanometer scale patterns. It is a simple nanolithography process with low cost, high throughput and high resolution. It creates patterns by mechanical deformation of imprint resist and subsequent processes. The imprint resist is typically a monomer or polymer formulation that is cured by heat or UV light during the imprinting. Adhesion between the resist and the template is controlled to allow proper release. There are many different types of nanoimprint lithography, including thermoplastic nanoimprint lithography and photo nanoimprint lithography.
Thermoplastic nanoimprint lithography (T-NIL) is the earliest nanoimprint lithography developed by Prof. Stephen Chou's group. In a standard T-NIL process, a thin layer of imprint resist (thermoplastic polymer) is spin coated onto the sample substrate. Then the mold, which has predefined topological patterns, and the sample are pressed together under a certain pressure. When the mold is heated to above the glass transition temperature of the polymer, the pattern on the mold is pressed into the softened polymer film. After cooling down, the mold is separated from the sample and the pattern resist is left on the substrate. A pattern transfer process (e.g. reactive ion etching) can be used to transfer the pattern in the resist to the underneath substrate.
In photo nanoimprint lithography (P-NIL), a photo (UV) curable liquid resist is applied to the sample substrate and the mold is normally made of transparent material (e.g. fused silica). After the mold and the substrate are pressed together, the resist is cured in UV light and solidifies. After mold separation, a similar pattern transfer process can be used to transfer the pattern in resist onto the underneath material.
However, the central goals in today's nanoimprint lithography are to make NIL appropriate for mass-productions by improving NIL performance and yield. Modification of raw materials is referred to as mold material and resist. The resist is usually employed as mask for different processes in lithography, because of the properties of thermal plastic, UV curing and easy removal such as PMMA, PS, and HSQ and so on. Otherwise, due to the resist's low modulus, poor solvent resistance, and high thermal expansion coefficient and uneasily patterned, these disadvantages lead to distortions and deformations of the resident imprinting nanostructures. As far as the materials for mold, quartz and Si or SiO2 wafer were usually applied, while this kind of mold generally fabricated by electronic beam lithography (EBL), it is easily crushed under high pressure.